src/main/java/org/apache/commons/collections4/map/LRUMap.java - commons-collections - Git at Google

 /*
  * Licensed to the Apache Software Foundation (ASF) under one or more
  * contributor license agreements.  See the NOTICE file distributed with
  * this work for additional information regarding copyright ownership.
  * The ASF licenses this file to You under the Apache License, Version 2.0
  * (the "License"); you may not use this file except in compliance with
  * the License.  You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package org.apache.commons.collections4.map;

 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.io.Serializable;
 import java.util.Map;

 import org.apache.commons.collections4.BoundedMap;

 /**
  * A {@code Map} implementation with a fixed maximum size which removes
  * the least recently used entry if an entry is added when full.
  * <p>
  * The least recently used algorithm works on the get and put operations only.
  * Iteration of any kind, including setting the value by iteration, does not
  * change the order. Queries such as containsKey and containsValue or access
  * via views also do not change the order.
  * </p>
  * <p>
  * A somewhat subtle ramification of the least recently used
  * algorithm is that calls to {@link #get(Object)} stand a very good chance
  * of modifying the map's iteration order and thus invalidating any
  * iterators currently in use.  It is therefore suggested that iterations
  * over an {@link LRUMap} instance access entry values only through a
  * {@link org.apache.commons.collections4.MapIterator MapIterator} or {@link #entrySet()} iterator.
  * </p>
  * <p>
  * The map implements {@code OrderedMap} and entries may be queried using
  * the bidirectional {@code OrderedMapIterator}. The order returned is
  * least recently used to most recently used. Iterators from map views can
  * also be cast to {@code OrderedIterator} if required.
  * </p>
  * <p>
  * All the available iterators can be reset back to the start by casting to
  * {@code ResettableIterator} and calling {@code reset()}.
  * </p>
  * <p>
  * <strong>Note that LRUMap is not synchronized and is not thread-safe.</strong>
  * If you wish to use this map from multiple threads concurrently, you must use
  * appropriate synchronization. The simplest approach is to wrap this map
  * using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw
  * {@code NullPointerException}'s when accessed by concurrent threads.
  * </p>
  *
  * @param <K> the type of the keys in this map
  * @param <V> the type of the values in this map
  * @since 3.0 (previously in main package v1.0)
  */
 public class LRUMap<K, V>
         extends AbstractLinkedMap<K, V> implements BoundedMap<K, V>, Serializable, Cloneable {

     /** Serialisation version */
     private static final long serialVersionUID = -612114643488955218L;
     /** Default maximum size */
     protected static final int DEFAULT_MAX_SIZE = 100;

     /** Maximum size */
     private transient int maxSize;
     /** Scan behavior */
     private boolean scanUntilRemovable;

     /**
      * Constructs a new empty map with a maximum size of 100.
      */
     public LRUMap() {
         this(DEFAULT_MAX_SIZE, DEFAULT_LOAD_FACTOR, false);
     }

     /**
      * Constructs a new, empty map with the specified maximum size.
      *
      * @param maxSize  the maximum size of the map
      * @throws IllegalArgumentException if the maximum size is less than one
      */
     public LRUMap(final int maxSize) {
         this(maxSize, DEFAULT_LOAD_FACTOR);
     }

     /**
      * Constructs a new, empty map with the specified maximum size.
      *
      * @param maxSize  the maximum size of the map
      * @param initialSize  the initial size of the map
      * @throws IllegalArgumentException if the maximum size is less than one
      * @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
      * @since 4.1
      */
     public LRUMap(final int maxSize, final int initialSize) {
         this(maxSize, initialSize, DEFAULT_LOAD_FACTOR);
     }

     /**
      * Constructs a new, empty map with the specified maximum size.
      *
      * @param maxSize  the maximum size of the map
      * @param scanUntilRemovable  scan until a removeable entry is found, default false
      * @throws IllegalArgumentException if the maximum size is less than one
      * @since 3.1
      */
     public LRUMap(final int maxSize, final boolean scanUntilRemovable) {
         this(maxSize, DEFAULT_LOAD_FACTOR, scanUntilRemovable);
     }

     /**
      * Constructs a new, empty map with the specified max capacity and
      * load factor.
      *
      * @param maxSize  the maximum size of the map
      * @param loadFactor  the load factor
      * @throws IllegalArgumentException if the maximum size is less than one
      * @throws IllegalArgumentException if the load factor is less than zero
      */
     public LRUMap(final int maxSize, final float loadFactor) {
         this(maxSize, loadFactor, false);
     }

     /**
      * Constructs a new, empty map with the specified max / initial capacity and
      * load factor.
      *
      * @param maxSize  the maximum size of the map
      * @param initialSize  the initial size of the map
      * @param loadFactor  the load factor
      * @throws IllegalArgumentException if the maximum size is less than one
      * @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
      * @throws IllegalArgumentException if the load factor is less than zero
      * @since 4.1
      */
     public LRUMap(final int maxSize, final int initialSize, final float loadFactor) {
         this(maxSize, initialSize, loadFactor, false);
     }

     /**
      * Constructs a new, empty map with the specified max capacity and load factor.
      *
      * @param maxSize  the maximum size of the map
      * @param loadFactor  the load factor
      * @param scanUntilRemovable  scan until a removeable entry is found, default false
      * @throws IllegalArgumentException if the maximum size is less than one
      * @throws IllegalArgumentException if the load factor is less than zero
      * @since 3.1
      */
     public LRUMap(final int maxSize, final float loadFactor, final boolean scanUntilRemovable) {
         this(maxSize, maxSize, loadFactor, scanUntilRemovable);
     }

     /**
      * Constructs a new, empty map with the specified max / initial capacity and load factor.
      *
      * @param maxSize  the maximum size of the map
      * @param initialSize  the initial size of the map
      * @param loadFactor  the load factor
      * @param scanUntilRemovable  scan until a removeable entry is found, default false
      * @throws IllegalArgumentException if the maximum size is less than one
      * @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
      * @throws IllegalArgumentException if the load factor is less than zero
      * @since 4.1
      */
     public LRUMap(final int maxSize,
                   final int initialSize,
                   final float loadFactor,
                   final boolean scanUntilRemovable) {

         super(initialSize, loadFactor);
         if (maxSize < 1) {
             throw new IllegalArgumentException("LRUMap max size must be greater than 0");
         }
         if (initialSize > maxSize) {
             throw new IllegalArgumentException("LRUMap initial size must not be greather than max size");
         }
         this.maxSize = maxSize;
         this.scanUntilRemovable = scanUntilRemovable;
     }

     /**
      * Constructor copying elements from another map.
      * <p>
      * The maximum size is set from the map's size.
      *
      * @param map  the map to copy
      * @throws NullPointerException if the map is null
      * @throws IllegalArgumentException if the map is empty
      */
     public LRUMap(final Map<? extends K, ? extends V> map) {
         this(map, false);
     }

     /**
      * Constructor copying elements from another map.
      *
      * <p>The maximum size is set from the map's size.</p>
      *
      * @param map  the map to copy
      * @param scanUntilRemovable  scan until a removeable entry is found, default false
      * @throws NullPointerException if the map is null
      * @throws IllegalArgumentException if the map is empty
      * @since 3.1
      */
     public LRUMap(final Map<? extends K, ? extends V> map, final boolean scanUntilRemovable) {
         this(map.size(), DEFAULT_LOAD_FACTOR, scanUntilRemovable);
         putAll(map);
     }

     //-----------------------------------------------------------------------
     /**
      * Gets the value mapped to the key specified.
      * <p>
      * This operation changes the position of the key in the map to the
      * most recently used position (last).
      *
      * @param key  the key
      * @return the mapped value, null if no match
      */
     @Override
     public V get(final Object key) {
         return get(key, true);
     }

     /**
      * Gets the value mapped to the key specified.
      * <p>
      * If {@code updateToMRU} is {@code true}, the position of the key in the map
      * is changed to the most recently used position (last), otherwise the iteration
      * order is not changed by this operation.
      *
      * @param key  the key
      * @param updateToMRU  whether the key shall be updated to the
      *   most recently used position
      * @return the mapped value, null if no match
      * @since 4.1
      */
     public V get(final Object key, final boolean updateToMRU) {
         final LinkEntry<K, V> entry = getEntry(key);
         if (entry == null) {
             return null;
         }
         if (updateToMRU) {
             moveToMRU(entry);
         }
         return entry.getValue();
     }

     //-----------------------------------------------------------------------
     /**
      * Moves an entry to the MRU position at the end of the list.
      * <p>
      * This implementation moves the updated entry to the end of the list.
      *
      * @param entry  the entry to update
      */
     protected void moveToMRU(final LinkEntry<K, V> entry) {
         if (entry.after != header) {
             modCount++;
             // remove
             if (entry.before == null) {
                 throw new IllegalStateException("Entry.before is null." +
                     " This should not occur if your keys are immutable, and you have used synchronization properly.");
             }
             entry.before.after = entry.after;
             entry.after.before = entry.before;
             // add first
             entry.after = header;
             entry.before = header.before;
             header.before.after = entry;
             header.before = entry;
         } else if (entry == header) {
             throw new IllegalStateException("Can't move header to MRU" +
                     " This should not occur if your keys are immutable, and you have used synchronization properly.");
         }
     }

     /**
      * Updates an existing key-value mapping.
      * <p>
      * This implementation moves the updated entry to the end of the list
      * using {@link #moveToMRU(AbstractLinkedMap.LinkEntry)}.
      *
      * @param entry  the entry to update
      * @param newValue  the new value to store
      */
     @Override
     protected void updateEntry(final HashEntry<K, V> entry, final V newValue) {
         moveToMRU((LinkEntry<K, V>) entry);  // handles modCount
         entry.setValue(newValue);
     }

     /**
      * Adds a new key-value mapping into this map.
      * <p>
      * This implementation checks the LRU size and determines whether to
      * discard an entry or not using {@link #removeLRU(AbstractLinkedMap.LinkEntry)}.
      * <p>
      * From Commons Collections 3.1 this method uses {@link #isFull()} rather
      * than accessing {@code size} and {@code maxSize} directly.
      * It also handles the scanUntilRemovable functionality.
      *
      * @param hashIndex  the index into the data array to store at
      * @param hashCode  the hash code of the key to add
      * @param key  the key to add
      * @param value  the value to add
      */
     @Override
     protected void addMapping(final int hashIndex, final int hashCode, final K key, final V value) {
         if (isFull()) {
             LinkEntry<K, V> reuse = header.after;
             boolean removeLRUEntry = false;
             if (scanUntilRemovable) {
                 while (reuse != header && reuse != null) {
                     if (removeLRU(reuse)) {
                         removeLRUEntry = true;
                         break;
                     }
                     reuse = reuse.after;
                 }
                 if (reuse == null) {
                     throw new IllegalStateException(
                         "Entry.after=null, header.after=" + header.after + " header.before=" + header.before +
                         " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                         " This should not occur if your keys are immutable and you used synchronization properly.");
                 }
             } else {
                 removeLRUEntry = removeLRU(reuse);
             }

             if (removeLRUEntry) {
                 if (reuse == null) {
                     throw new IllegalStateException(
                         "reuse=null, header.after=" + header.after + " header.before=" + header.before +
                         " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                         " This should not occur if your keys are immutable and you used synchronization properly.");
                 }
                 reuseMapping(reuse, hashIndex, hashCode, key, value);
             } else {
                 super.addMapping(hashIndex, hashCode, key, value);
             }
         } else {
             super.addMapping(hashIndex, hashCode, key, value);
         }
     }

     /**
      * Reuses an entry by removing it and moving it to a new place in the map.
      * <p>
      * This method uses {@link #removeEntry}, {@link #reuseEntry} and {@link #addEntry}.
      *
      * @param entry  the entry to reuse
      * @param hashIndex  the index into the data array to store at
      * @param hashCode  the hash code of the key to add
      * @param key  the key to add
      * @param value  the value to add
      */
     protected void reuseMapping(final LinkEntry<K, V> entry, final int hashIndex, final int hashCode,
                                 final K key, final V value) {
         // find the entry before the entry specified in the hash table
         // remember that the parameters (except the first) refer to the new entry,
         // not the old one
         try {
             final int removeIndex = hashIndex(entry.hashCode, data.length);
             final HashEntry<K, V>[] tmp = data;  // may protect against some sync issues
             HashEntry<K, V> loop = tmp[removeIndex];
             HashEntry<K, V> previous = null;
             while (loop != entry && loop != null) {
                 previous = loop;
                 loop = loop.next;
             }
             if (loop == null) {
                 throw new IllegalStateException(
                     "Entry.next=null, data[removeIndex]=" + data[removeIndex] + " previous=" + previous +
                     " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                     " This should not occur if your keys are immutable, and you have used synchronization properly.");
             }

             // reuse the entry
             modCount++;
             removeEntry(entry, removeIndex, previous);
             reuseEntry(entry, hashIndex, hashCode, key, value);
             addEntry(entry, hashIndex);
         } catch (final NullPointerException ex) {
             throw new IllegalStateException(
                     "NPE, entry=" + entry + " entryIsHeader=" + (entry==header) +
                     " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                     " This should not occur if your keys are immutable, and you have used synchronization properly.");
         }
     }

     /**
      * Subclass method to control removal of the least recently used entry from the map.
      * <p>
      * This method exists for subclasses to override. A subclass may wish to
      * provide cleanup of resources when an entry is removed. For example:
      * <pre>
      * protected boolean removeLRU(LinkEntry entry) {
      *   releaseResources(entry.getValue());  // release resources held by entry
      *   return true;  // actually delete entry
      * }
      * </pre>
      * <p>
      * Alternatively, a subclass may choose to not remove the entry or selectively
      * keep certain LRU entries. For example:
      * <pre>
      * protected boolean removeLRU(LinkEntry entry) {
      *   if (entry.getKey().toString().startsWith("System.")) {
      *     return false;  // entry not removed from LRUMap
      *   } else {
      *     return true;  // actually delete entry
      *   }
      * }
      * </pre>
      * The effect of returning false is dependent on the scanUntilRemovable flag.
      * If the flag is true, the next LRU entry will be passed to this method and so on
      * until one returns false and is removed, or every entry in the map has been passed.
      * If the scanUntilRemovable flag is false, the map will exceed the maximum size.
      * <p>
      * NOTE: Commons Collections 3.0 passed the wrong entry to this method.
      * This is fixed in version 3.1 onwards.
      *
      * @param entry  the entry to be removed
      * @return {@code true}
      */
     protected boolean removeLRU(final LinkEntry<K, V> entry) {
         return true;
     }

     //-----------------------------------------------------------------------
     /**
      * Returns true if this map is full and no new mappings can be added.
      *
      * @return {@code true} if the map is full
      */
     @Override
     public boolean isFull() {
         return size >= maxSize;
     }

     /**
      * Gets the maximum size of the map (the bound).
      *
      * @return the maximum number of elements the map can hold
      */
     @Override
     public int maxSize() {
         return maxSize;
     }

     /**
      * Whether this LRUMap will scan until a removable entry is found when the
      * map is full.
      *
      * @return true if this map scans
      * @since 3.1
      */
     public boolean isScanUntilRemovable() {
         return scanUntilRemovable;
     }

     //-----------------------------------------------------------------------
     /**
      * Clones the map without cloning the keys or values.
      *
      * @return a shallow clone
      */
     @Override
     public LRUMap<K, V> clone() {
         return (LRUMap<K, V>) super.clone();
     }

     /**
      * Write the map out using a custom routine.
      *
      * @param out  the output stream
      * @throws IOException if an error occurs while writing to the stream
      */
     private void writeObject(final ObjectOutputStream out) throws IOException {
         out.defaultWriteObject();
         doWriteObject(out);
     }

     /**
      * Read the map in using a custom routine.
      *
      * @param in the input stream
      * @throws IOException if an error occurs while reading from the stream
      * @throws ClassNotFoundException if an object read from the stream can not be loaded
      */
     private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
         in.defaultReadObject();
         doReadObject(in);
     }

     /**
      * Writes the data necessary for {@code put()} to work in deserialization.
      *
      * @param out  the output stream
      * @throws IOException if an error occurs while writing to the stream
      */
     @Override
     protected void doWriteObject(final ObjectOutputStream out) throws IOException {
         out.writeInt(maxSize);
         super.doWriteObject(out);
     }

     /**
      * Reads the data necessary for {@code put()} to work in the superclass.
      *
      * @param in  the input stream
      * @throws IOException if an error occurs while reading from the stream
      * @throws ClassNotFoundException if an object read from the stream can not be loaded
      */
     @Override
     protected void doReadObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
         maxSize = in.readInt();
         super.doReadObject(in);
     }

 }
	/*
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package org.apache.commons.collections4.map;

	import java.io.IOException;
	import java.io.ObjectInputStream;
	import java.io.ObjectOutputStream;
	import java.io.Serializable;
	import java.util.Map;

	import org.apache.commons.collections4.BoundedMap;

	/**
	* A {@code Map} implementation with a fixed maximum size which removes
	* the least recently used entry if an entry is added when full.
	* <p>
	* The least recently used algorithm works on the get and put operations only.
	* Iteration of any kind, including setting the value by iteration, does not
	* change the order. Queries such as containsKey and containsValue or access
	* via views also do not change the order.
	* </p>
	* <p>
	* A somewhat subtle ramification of the least recently used
	* algorithm is that calls to {@link #get(Object)} stand a very good chance
	* of modifying the map's iteration order and thus invalidating any
	* iterators currently in use. It is therefore suggested that iterations
	* over an {@link LRUMap} instance access entry values only through a
	* {@link org.apache.commons.collections4.MapIterator MapIterator} or {@link #entrySet()} iterator.
	* </p>
	* <p>
	* The map implements {@code OrderedMap} and entries may be queried using
	* the bidirectional {@code OrderedMapIterator}. The order returned is
	* least recently used to most recently used. Iterators from map views can
	* also be cast to {@code OrderedIterator} if required.
	* </p>
	* <p>
	* All the available iterators can be reset back to the start by casting to
	* {@code ResettableIterator} and calling {@code reset()}.
	* </p>
	* <p>
	* <strong>Note that LRUMap is not synchronized and is not thread-safe.</strong>
	* If you wish to use this map from multiple threads concurrently, you must use
	* appropriate synchronization. The simplest approach is to wrap this map
	* using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw
	* {@code NullPointerException}'s when accessed by concurrent threads.
	* </p>
	*
	* @param <K> the type of the keys in this map
	* @param <V> the type of the values in this map
	* @since 3.0 (previously in main package v1.0)
	*/
	public class LRUMap<K, V>
	extends AbstractLinkedMap<K, V> implements BoundedMap<K, V>, Serializable, Cloneable {

	/** Serialisation version */
	private static final long serialVersionUID = -612114643488955218L;
	/** Default maximum size */
	protected static final int DEFAULT_MAX_SIZE = 100;

	/** Maximum size */
	private transient int maxSize;
	/** Scan behavior */
	private boolean scanUntilRemovable;

	/**
	* Constructs a new empty map with a maximum size of 100.
	*/
	public LRUMap() {
	this(DEFAULT_MAX_SIZE, DEFAULT_LOAD_FACTOR, false);
	}

	/**
	* Constructs a new, empty map with the specified maximum size.
	*
	* @param maxSize the maximum size of the map
	* @throws IllegalArgumentException if the maximum size is less than one
	*/
	public LRUMap(final int maxSize) {
	this(maxSize, DEFAULT_LOAD_FACTOR);
	}

	/**
	* Constructs a new, empty map with the specified maximum size.
	*
	* @param maxSize the maximum size of the map
	* @param initialSize the initial size of the map
	* @throws IllegalArgumentException if the maximum size is less than one
	* @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
	* @since 4.1
	*/
	public LRUMap(final int maxSize, final int initialSize) {
	this(maxSize, initialSize, DEFAULT_LOAD_FACTOR);
	}

	/**
	* Constructs a new, empty map with the specified maximum size.
	*
	* @param maxSize the maximum size of the map
	* @param scanUntilRemovable scan until a removeable entry is found, default false
	* @throws IllegalArgumentException if the maximum size is less than one
	* @since 3.1
	*/
	public LRUMap(final int maxSize, final boolean scanUntilRemovable) {
	this(maxSize, DEFAULT_LOAD_FACTOR, scanUntilRemovable);
	}

	/**
	* Constructs a new, empty map with the specified max capacity and
	* load factor.
	*
	* @param maxSize the maximum size of the map
	* @param loadFactor the load factor
	* @throws IllegalArgumentException if the maximum size is less than one
	* @throws IllegalArgumentException if the load factor is less than zero
	*/
	public LRUMap(final int maxSize, final float loadFactor) {
	this(maxSize, loadFactor, false);
	}

	/**
	* Constructs a new, empty map with the specified max / initial capacity and
	* load factor.
	*
	* @param maxSize the maximum size of the map
	* @param initialSize the initial size of the map
	* @param loadFactor the load factor
	* @throws IllegalArgumentException if the maximum size is less than one
	* @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
	* @throws IllegalArgumentException if the load factor is less than zero
	* @since 4.1
	*/
	public LRUMap(final int maxSize, final int initialSize, final float loadFactor) {
	this(maxSize, initialSize, loadFactor, false);
	}

	/**
	* Constructs a new, empty map with the specified max capacity and load factor.
	*
	* @param maxSize the maximum size of the map
	* @param loadFactor the load factor
	* @param scanUntilRemovable scan until a removeable entry is found, default false
	* @throws IllegalArgumentException if the maximum size is less than one
	* @throws IllegalArgumentException if the load factor is less than zero
	* @since 3.1
	*/
	public LRUMap(final int maxSize, final float loadFactor, final boolean scanUntilRemovable) {
	this(maxSize, maxSize, loadFactor, scanUntilRemovable);
	}

	/**
	* Constructs a new, empty map with the specified max / initial capacity and load factor.
	*
	* @param maxSize the maximum size of the map
	* @param initialSize the initial size of the map
	* @param loadFactor the load factor
	* @param scanUntilRemovable scan until a removeable entry is found, default false
	* @throws IllegalArgumentException if the maximum size is less than one
	* @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
	* @throws IllegalArgumentException if the load factor is less than zero
	* @since 4.1
	*/
	public LRUMap(final int maxSize,
	final int initialSize,
	final float loadFactor,
	final boolean scanUntilRemovable) {

	super(initialSize, loadFactor);
	if (maxSize < 1) {
	throw new IllegalArgumentException("LRUMap max size must be greater than 0");
	}
	if (initialSize > maxSize) {
	throw new IllegalArgumentException("LRUMap initial size must not be greather than max size");
	}
	this.maxSize = maxSize;
	this.scanUntilRemovable = scanUntilRemovable;
	}

	/**
	* Constructor copying elements from another map.
	* <p>
	* The maximum size is set from the map's size.
	*
	* @param map the map to copy
	* @throws NullPointerException if the map is null
	* @throws IllegalArgumentException if the map is empty
	*/
	public LRUMap(final Map<? extends K, ? extends V> map) {
	this(map, false);
	}

	/**
	* Constructor copying elements from another map.
	*
	* <p>The maximum size is set from the map's size.</p>
	*
	* @param map the map to copy
	* @param scanUntilRemovable scan until a removeable entry is found, default false
	* @throws NullPointerException if the map is null
	* @throws IllegalArgumentException if the map is empty
	* @since 3.1
	*/
	public LRUMap(final Map<? extends K, ? extends V> map, final boolean scanUntilRemovable) {
	this(map.size(), DEFAULT_LOAD_FACTOR, scanUntilRemovable);
	putAll(map);
	}

	//-----------------------------------------------------------------------
	/**
	* Gets the value mapped to the key specified.
	* <p>
	* This operation changes the position of the key in the map to the
	* most recently used position (last).
	*
	* @param key the key
	* @return the mapped value, null if no match
	*/
	@Override
	public V get(final Object key) {
	return get(key, true);
	}

	/**
	* Gets the value mapped to the key specified.
	* <p>
	* If {@code updateToMRU} is {@code true}, the position of the key in the map
	* is changed to the most recently used position (last), otherwise the iteration
	* order is not changed by this operation.
	*
	* @param key the key
	* @param updateToMRU whether the key shall be updated to the
	* most recently used position
	* @return the mapped value, null if no match
	* @since 4.1
	*/
	public V get(final Object key, final boolean updateToMRU) {
	final LinkEntry<K, V> entry = getEntry(key);
	if (entry == null) {
	return null;
	}
	if (updateToMRU) {
	moveToMRU(entry);
	}
	return entry.getValue();
	}

	//-----------------------------------------------------------------------
	/**
	* Moves an entry to the MRU position at the end of the list.
	* <p>
	* This implementation moves the updated entry to the end of the list.
	*
	* @param entry the entry to update
	*/
	protected void moveToMRU(final LinkEntry<K, V> entry) {
	if (entry.after != header) {
	modCount++;
	// remove
	if (entry.before == null) {
	throw new IllegalStateException("Entry.before is null." +
	" This should not occur if your keys are immutable, and you have used synchronization properly.");
	}
	entry.before.after = entry.after;
	entry.after.before = entry.before;
	// add first
	entry.after = header;
	entry.before = header.before;
	header.before.after = entry;
	header.before = entry;
	} else if (entry == header) {
	throw new IllegalStateException("Can't move header to MRU" +
	" This should not occur if your keys are immutable, and you have used synchronization properly.");
	}
	}

	/**
	* Updates an existing key-value mapping.
	* <p>
	* This implementation moves the updated entry to the end of the list
	* using {@link #moveToMRU(AbstractLinkedMap.LinkEntry)}.
	*
	* @param entry the entry to update
	* @param newValue the new value to store
	*/
	@Override
	protected void updateEntry(final HashEntry<K, V> entry, final V newValue) {
	moveToMRU((LinkEntry<K, V>) entry); // handles modCount
	entry.setValue(newValue);
	}

	/**
	* Adds a new key-value mapping into this map.
	* <p>
	* This implementation checks the LRU size and determines whether to
	* discard an entry or not using {@link #removeLRU(AbstractLinkedMap.LinkEntry)}.
	* <p>
	* From Commons Collections 3.1 this method uses {@link #isFull()} rather
	* than accessing {@code size} and {@code maxSize} directly.
	* It also handles the scanUntilRemovable functionality.
	*
	* @param hashIndex the index into the data array to store at
	* @param hashCode the hash code of the key to add
	* @param key the key to add
	* @param value the value to add
	*/
	@Override
	protected void addMapping(final int hashIndex, final int hashCode, final K key, final V value) {
	if (isFull()) {
	LinkEntry<K, V> reuse = header.after;
	boolean removeLRUEntry = false;
	if (scanUntilRemovable) {
	while (reuse != header && reuse != null) {
	if (removeLRU(reuse)) {
	removeLRUEntry = true;
	break;
	}
	reuse = reuse.after;
	}
	if (reuse == null) {
	throw new IllegalStateException(
	"Entry.after=null, header.after=" + header.after + " header.before=" + header.before +
	" key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
	" This should not occur if your keys are immutable and you used synchronization properly.");
	}
	} else {
	removeLRUEntry = removeLRU(reuse);
	}

	if (removeLRUEntry) {
	if (reuse == null) {
	throw new IllegalStateException(
	"reuse=null, header.after=" + header.after + " header.before=" + header.before +
	" key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
	" This should not occur if your keys are immutable and you used synchronization properly.");
	}
	reuseMapping(reuse, hashIndex, hashCode, key, value);
	} else {
	super.addMapping(hashIndex, hashCode, key, value);
	}
	} else {
	super.addMapping(hashIndex, hashCode, key, value);
	}
	}

	/**
	* Reuses an entry by removing it and moving it to a new place in the map.
	* <p>
	* This method uses {@link #removeEntry}, {@link #reuseEntry} and {@link #addEntry}.
	*
	* @param entry the entry to reuse
	* @param hashIndex the index into the data array to store at
	* @param hashCode the hash code of the key to add
	* @param key the key to add
	* @param value the value to add
	*/
	protected void reuseMapping(final LinkEntry<K, V> entry, final int hashIndex, final int hashCode,
	final K key, final V value) {
	// find the entry before the entry specified in the hash table
	// remember that the parameters (except the first) refer to the new entry,
	// not the old one
	try {
	final int removeIndex = hashIndex(entry.hashCode, data.length);
	final HashEntry<K, V>[] tmp = data; // may protect against some sync issues
	HashEntry<K, V> loop = tmp[removeIndex];
	HashEntry<K, V> previous = null;
	while (loop != entry && loop != null) {
	previous = loop;
	loop = loop.next;
	}
	if (loop == null) {
	throw new IllegalStateException(
	"Entry.next=null, data[removeIndex]=" + data[removeIndex] + " previous=" + previous +
	" key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
	" This should not occur if your keys are immutable, and you have used synchronization properly.");
	}

	// reuse the entry
	modCount++;
	removeEntry(entry, removeIndex, previous);
	reuseEntry(entry, hashIndex, hashCode, key, value);
	addEntry(entry, hashIndex);
	} catch (final NullPointerException ex) {
	throw new IllegalStateException(
	"NPE, entry=" + entry + " entryIsHeader=" + (entry==header) +
	" key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
	" This should not occur if your keys are immutable, and you have used synchronization properly.");
	}
	}

	/**
	* Subclass method to control removal of the least recently used entry from the map.
	* <p>
	* This method exists for subclasses to override. A subclass may wish to
	* provide cleanup of resources when an entry is removed. For example:
	* <pre>
	* protected boolean removeLRU(LinkEntry entry) {
	* releaseResources(entry.getValue()); // release resources held by entry
	* return true; // actually delete entry
	* }
	* </pre>
	* <p>
	* Alternatively, a subclass may choose to not remove the entry or selectively
	* keep certain LRU entries. For example:
	* <pre>
	* protected boolean removeLRU(LinkEntry entry) {
	* if (entry.getKey().toString().startsWith("System.")) {
	* return false; // entry not removed from LRUMap
	* } else {
	* return true; // actually delete entry
	* }
	* }
	* </pre>
	* The effect of returning false is dependent on the scanUntilRemovable flag.
	* If the flag is true, the next LRU entry will be passed to this method and so on
	* until one returns false and is removed, or every entry in the map has been passed.
	* If the scanUntilRemovable flag is false, the map will exceed the maximum size.
	* <p>
	* NOTE: Commons Collections 3.0 passed the wrong entry to this method.
	* This is fixed in version 3.1 onwards.
	*
	* @param entry the entry to be removed
	* @return {@code true}
	*/
	protected boolean removeLRU(final LinkEntry<K, V> entry) {
	return true;
	}

	//-----------------------------------------------------------------------
	/**
	* Returns true if this map is full and no new mappings can be added.
	*
	* @return {@code true} if the map is full
	*/
	@Override
	public boolean isFull() {
	return size >= maxSize;
	}

	/**
	* Gets the maximum size of the map (the bound).
	*
	* @return the maximum number of elements the map can hold
	*/
	@Override
	public int maxSize() {
	return maxSize;
	}

	/**
	* Whether this LRUMap will scan until a removable entry is found when the
	* map is full.
	*
	* @return true if this map scans
	* @since 3.1
	*/
	public boolean isScanUntilRemovable() {
	return scanUntilRemovable;
	}

	//-----------------------------------------------------------------------
	/**
	* Clones the map without cloning the keys or values.
	*
	* @return a shallow clone
	*/
	@Override
	public LRUMap<K, V> clone() {
	return (LRUMap<K, V>) super.clone();
	}

	/**
	* Write the map out using a custom routine.
	*
	* @param out the output stream
	* @throws IOException if an error occurs while writing to the stream
	*/
	private void writeObject(final ObjectOutputStream out) throws IOException {
	out.defaultWriteObject();
	doWriteObject(out);
	}

	/**
	* Read the map in using a custom routine.
	*
	* @param in the input stream
	* @throws IOException if an error occurs while reading from the stream
	* @throws ClassNotFoundException if an object read from the stream can not be loaded
	*/
	private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
	in.defaultReadObject();
	doReadObject(in);
	}

	/**
	* Writes the data necessary for {@code put()} to work in deserialization.
	*
	* @param out the output stream
	* @throws IOException if an error occurs while writing to the stream
	*/
	@Override
	protected void doWriteObject(final ObjectOutputStream out) throws IOException {
	out.writeInt(maxSize);
	super.doWriteObject(out);
	}

	/**
	* Reads the data necessary for {@code put()} to work in the superclass.
	*
	* @param in the input stream
	* @throws IOException if an error occurs while reading from the stream
	* @throws ClassNotFoundException if an object read from the stream can not be loaded
	*/
	@Override
	protected void doReadObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
	maxSize = in.readInt();
	super.doReadObject(in);
	}

	}